It is often necessary to surgically treat spinal disorders such as scoliosis. Numerous systems for use in spinal correction and fixation have been disclosed. These systems usually include a pair of elongate members, typically either rods or plates, placed along the vertebral column. For the sake of simplicity, the term “rod” is used throughout to refer to any elongate member. Each rod is attached to the spine with various attachment devices. These attachment devices may include, but are not limited to, pedicle screws, plates, transverse process hooks, sublaminar hooks, pedicle hooks, and other similar devices.
It is also well known that the strength and stability of the dual rod assembly can be increased by coupling the two rods with a cross-brace or transconnector which extends substantially horizontal to the longitudinal axes of the rods across the spine. The simplest situation in which a transconnector could be used occurs when the two rods are geometrically aligned. Specifically, the two rods are parallel to each other, i.e. there is no rod convergence or divergence in the medial-lateral direction; the two rods have the same orientation with respect to the coronal plane (viewed in the anterior-posterior direction), i.e. the rods are coplanar from a lateral view; and the two rods are located a uniform distance from each other.
Due to a wide variety of factors, the two rods are rarely three dimensionally geometrically aligned in clinical situations. There are several ways to address the variations of geometrical alignment. First, one or both of the rods can be bent to accommodate the transconnector. However, any bending in either of the rods can adversely affect the fixation to the spine and comprise clinical outcome. Furthermore, the bending can also adversely affect the mechanical properties of the rods. The transconnector can also be bent so that the disturbance to the rod positioning is minimized. As is the case with bending of the rods, the mechanical properties of the transconnector could be compromised.
Transconnectors with some adjustability have been designed to adapt for variations from geometrical alignment. However, most are multi-piece systems that can be difficult to assemble and use in the surgical environment. U.S. Pat. No. 5,980,523 discloses a multi-piece transverse connector for spinal rods that can accommodate converging or diverging rods. However, accidental disassembly of the connector by the surgeon is possible. Even those that are one-piece designs do not allow for adjustments to compensate for all three modes in which there may be variation from geometrical alignment: convergence or divergence, non-coplanar rods, and variability in rod separation distances. For example, U.S. Pat. No. 5,947,966 discloses a device for linking adjacent spinal rods. In one embodiment, the device includes two members that are movable with respect to one another to accommodate different rod separation distances. A pin on one member engages a groove on the other member to provisionally couple the two members, thereby preventing a surgeon from separating the two members. Because the pin is sized to exactly fit the groove, no movement of the pin transverse to the longitudinal axis of the groove is possible. As a result, the device disclosed in the '966 patent cannot accommodate non-coplanar rods or adjust for rod convergence or divergence.
Thus, there exists a need for an improved transconnector for coupling spinal rods.